JPH0878739A - Superconductive junction device and its manufacturing method - Google Patents

Abstract

PURPOSE: To provide a superconductive junction device which can be utilized by an inexpensive liquid nitrogen and a simple cooler and to provide a superconductive junction device which has a junction to be controlled easily when it is manufactured and can be relatively easily manufactured and its manufacturing method. CONSTITUTION: In a superconductive junction device and its manufacturing method, the superconductive junction device consists of copper oxide superconductive material containing carbon group, the junction part contains one portion of the composition of the copper oxide superconductive material constituting the superconductive part, and the carbonic acid group consists of a non-conductive material which is contained more than the superconductive material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting junction device and a method of manufacturing the same, and more particularly, to a Josephson junction or a Josephson computer using a Josephson junction, a mixer, an SQUID, a sensor, a switching element and the like. The present invention relates to a superconducting junction device which can be used not only in the devices described above but also in a system incorporating those devices, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, a compound oxide superconductor containing copper having an extremely high superconducting transition temperature has been invented and attracted attention.
Typical materials thereof are, for example, YBa ₂ Cu ₃ O ₇ which is a YBCO type material and Bi ₂ Sr ₂ C which is a Bi type material.
Examples include a _n Cu _{n + 1} O _y (n = 0, 1, 2) and Tl ₂ Ba ₂ C _n Cu _{n + 1} O _y (n = 0, 1, 2) which is a Tl-based material. With the invention of these material systems, the superconducting state can be obtained with inexpensive liquid nitrogen or a simple cooler without using expensive liquid helium as a cryogenic agent, so the application of Josephson devices can be extended to consumer products. The sex is coming out. or,
Various superconducting junction devices using these complex oxide superconductors containing copper have been devised. Among them, what is known as the Josephson junction mostly uses grain boundaries. It is a weak bond. This grain boundary Josephson junction is a large number of grain boundary junctions that are naturally generated, and SQUIDs have been prototyped using this.

In addition, in the stacked type superconducting tunnel type Josephson junction, a junction having a barrier layer between the upper and lower electrodes is generally used, and various methods have been tried in this type. For example, a composite oxide superconductor containing copper is used for the lower electrode layer, a conventionally known metal-based superconductor is used for the upper electrode layer, and a lower layer is used for forming the upper electrode on the barrier layer. There is a type of oxide superconductor-degraded film-metal superconductor, which attempts to utilize the deterioration of the interface between the electrode and the electrode. In addition, this type of upper electrode is simply
There is also a SIN type tunnel junction composed of an oxide superconductor-degraded film-metal, which is a metal such as u. Furthermore,
A full-scale SIS type of oxide superconductor-oxide barrier layer-oxide superconductor using an oxide for the barrier layer has been proposed. As a material system tried in this SIS type, a YBCO material is used for the superconducting layer and PrBa ₂ Cu ₃ O ₇ is used for the oxide barrier layer, and
Using Bi ₂ Sr ₂ CaCu ₂ O _y in the superconducting layer, and although the oxide barrier layer, and the like that use the Bi ₂ Sr ₂ CuO _y, both have been the good tunneling Josephson element Absent.

[0004]

In the Josephson junction using the crystal grain boundaries of the superconductor among the above-mentioned conventional examples, although the joint portion is relatively easy to fabricate, the joint portion is accidentally produced. Accordingly, there is a problem that it is not suitable for application. In the present situation, a tunnel type Josephson junction that uses grain boundaries cannot be manufactured as a controlled one in a high temperature superconductor. Further, in the laminated tunnel type Josephson junction of the above-mentioned conventional examples, since the conventional metal-based superconductor is used for the upper electrode layer, the operating temperature becomes equal to or lower than the transition temperature of the metal-based superconductor. As a result, there was a problem that liquid helium was necessary. Further, the SIN type tunnel junction using a metal for the upper electrode layer is inferior in device characteristics to the SIS type.

In the most preferred SIS type conventional example,
When PrBa ₂ Cu ₃ O ₇ is used for the oxide barrier layer,
Alternatively, when Bi ₂ Sr ₂ CuO _y is used, the oxide barrier layer becomes a semiconductor or a metal, resulting in an SNS type junction, and a good SIS type having an insulating oxide barrier layer. The current situation is that the joining of the above has not been obtained yet. Further, methods of using other oxides such as MgO for the oxide barrier layer have also been investigated, but when these oxides are used for the oxide barrier layer, a composite oxide containing copper for the electrode layer is used. At present, a good interface is not obtained due to the difference in crystal structure between the superconductor and the oxide barrier layer or the difference in film forming temperature. Therefore, an object of the present invention is to provide a superconducting junction device that can be used with inexpensive liquid nitrogen or a simple cooler. Another object of the present invention is to provide a superconducting junction device which has a joint part which can be easily controlled at the time of manufacture and which is relatively easy to manufacture, and a manufacturing method thereof.

[0006]

The above object can be achieved by the present invention described below. That is, the present invention is a superconducting junction device including a superconducting portion and a joint portion, wherein the superconducting portion is made of a copper oxide superconducting material containing a carbonate group, and the joint portion constitutes the superconducting portion. A superconducting junction device having a part of the composition of a copper oxide superconducting material, and consisting of a non-superconducting material containing more carbonic acid groups in the composition than the superconducting material, and That is the manufacturing method.

[0007]

In the superconducting junction device of the present invention, since the material having the same element is used for the superconducting electrode portion and the joint portion, there is a problem of interface deterioration due to diffusion of elements which occurs when the joint portion is formed. Will be resolved. Further, since a high resistance carbonate is used for the joint portion, good superconducting device characteristics are expected. Furthermore, since the characteristics of the junction can be controlled by the annealing conditions after film formation, the characteristics of the element can be easily controlled. The annealing conditions here mainly include oxygen partial pressure, carbon dioxide partial pressure, annealing temperature and cooling rate after annealing.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail with reference to preferred embodiments. The superconducting junction device of the present invention is a superconducting junction device comprising a superconducting portion and a joint portion, wherein the superconducting portion is made of a copper oxide superconducting material containing a carbonate group, and the joint portion is the superconducting portion. Is composed of a non-superconducting material having a part of the composition of the copper oxide superconducting material, and having a carbonate group in the composition in a larger amount than that of the superconducting material. In a further preferred embodiment,
As a copper oxide superconducting material containing a carbonic acid group that constitutes the superconducting portion, one represented by the following general formula is used. Ln _a Ca _b Sr _c Bad _d Cu _{2 + e} O _{6 + f} C _g (In the formula, a + b + c + d = 3, and 0.2 ≦ a ≦ 0.
8 and 0.2 ≦ b ≦ 1.0 and 0.5 ≦ c ≦ 2.
2, 0 ≦ d ≦ 1.6, 0 ≦ e ≦ 0.8, and 0
<F <2 and 0.2 ≦ g ≦ 1), and the non-superconducting material forming the joint is selected from the group consisting of the general formula MCO ₃ (wherein M is Ca, Sr and Ba). And one or more elements or atomic groups). or,
The method for producing the above superconducting junction device of the present invention is
The method is characterized by having a step of heat-treating the superconducting junction in an atmosphere in which carbon dioxide and oxygen are mixed.

As the material of the superconducting electrode portion constituting the superconducting junction device of the present invention, any material is preferably used as long as it is a copper oxide superconducting material containing a carbonic acid group. It is more preferable to use a high temperature superconducting oxide material. In addition, the material used for the joint portion that constitutes the superconducting junction device of the present invention is the same as some of the elements used for the superconductor that constitutes the above-mentioned superconducting electrode portion. It is preferable to use a non-superconducting material that has a carbonic acid group, which is more contained than the forming material of the superconducting layer, especially in view of ease of control and high resistivity. It is preferable to configure.

In the superconducting junction device of the present invention, in particular, the so-called 12 superconducting layer having a high superconducting transition temperature is used.
It is preferable to use a material having a 12 structure, but as such a material having a 1212 structure, a composition formula Ln _{a
Ca b Sr c Ba d Cu 2} + e O 6 + f material represented by C _g and the like. On the other hand, when a material having a 1212 structure having the above-mentioned composition is selected as the material for forming the superconducting layer, the composition of the constituent material of the joint is MCO ₃ (where M is Ca,
(One or more elements or atomic groups selected from Sr and Ba)
Then, the material not only utilizes the same elements as those used for the constituent material of the superconducting layer described above, but also has a very high resistance and is This is particularly preferable because the characteristics can be well controlled in the annealing process after film formation.

Generally, the characteristics of the grain boundaries between the superconducting layer and the junction are generally determined at the time of film formation. However, like the superconducting junction device of the present invention, the superconducting layer and the junction are formed. When both the materials to be used contain a carbonate group, it is possible to control the characteristics of the crystal grain boundaries of the junction in the annealing process performed after the film formation. That is, this is because it is possible to grow or eliminate the insulating layer at the junction at the crystal grain boundary between the superconducting layer and the junction in an atmosphere of oxygen and carbon dioxide. For example, in the annealing process performed after film formation, if the annealing temperature is low, the carbon dioxide partial pressure is high, or the cooling rate is slow, the growth of the insulating layer at the junction is promoted, and conversely the oxygen content is increased. High pressure,
When the annealing temperature is high and the cooling rate is high, carbonic acid groups escape from the material forming the joint, and as a result, the insulating layer itself at the joint disappears. It is considered that this action occurs reversibly, and because it occurs at the crystal grain boundaries where carbon dioxide and oxygen can flow in and out, the characteristics of the joint can be controlled by changing the annealing conditions variously. .

As described above, in the present invention, by selecting the materials as described above, a barrier layer having a high insulating property, which has not been obtained in the past, can be obtained very well, and the bondability of the interface and further As a result of improving the controllability, it can be used not only for the grain boundary junction type Josephson element of the complex oxide superconductor containing copper but also for the tunnel type Josephson junction element. Also, as a superconductor used for the superconducting layer, 1
If a high-temperature superconducting material having a structure of 212 is selected, it can be used not only in liquid nitrogen but also in a simple cooler because the superconducting transition temperature is high. Although the microbridge type is suitable for the shape of the obtained element, it is also possible to make a long and narrow pattern such as a snake pattern and use a large number of resulting Josephson junctions as a device. In addition, a general film forming apparatus such as a physical vapor deposition method or a chemical vapor deposition method can be used for manufacturing the superconducting junction device of the present invention.

[0013]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 FIG. 1 shows a sectional view of a superconducting junction device of an example according to the present invention. In the figure, 11 is a superconducting thin film, 12 is a junction, 13 is a MgO substrate, 14 is an electrode, 15 is a current monitor, and 16 is a drive power supply. As a method for manufacturing the superconducting junction device shown in FIG. 1, first, a composite oxide superconductor material Y _0.5 Ca _0.5 Sr _0.7 Ba _1.3 Cu _2.6 O ₇ C was used.
_0.4 for MgO substrate 1 by magnetron sputtering method
A superconducting thin film 11 was formed by depositing a film on the substrate 3 at a substrate temperature of 800 degrees so as to have a film thickness of 400 nm. After the film formation, a bridge 12 having a width of 10 μm and a length of 10 μm was formed on the superconducting thin film 11 formed above by a photolithography method. Further, after the annealing treatment, the electrode 14 was attached, and the superconducting junction device of the present invention having a cross section as shown in FIG. 1 was produced. FIG. 2 shows a schematic view of a crystal grain boundary in which the portion of the bridge 12 is enlarged. In the figure, 21 is a crystal grain, 22 is a bonding portion, and 23 is a substrate.

Next, in order to evaluate the influence of annealing conditions (annealing temperature, oxygen partial pressure, carbon dioxide partial pressure, cooling rate) on the device characteristics, as shown in Table 1, the annealing treatment after film formation is performed. The element characteristics of each of the obtained superconducting junction devices were examined by the following methods under various conditions. In order to evaluate the element characteristics of the superconducting junction device, the electrode 14
Then, a gold wire is attached as shown in FIG. 1, and the direct current-voltage characteristic is 4.2 to 4.2 by the drive power source 16 and the current monitor 15.
It was measured in the temperature range of 80K. Table 1 shows the obtained evaluation results.

For comparison, No. 1 in Table 1 shows the evaluation result in the case where the annealing treatment is not performed after the film formation. As shown in Table 1, in this case, the junction is merely ohmic. However, it was not a Josephson junction. In addition, when this junction was analyzed by EPMA,
No grain boundary junction containing excess carbonate groups was observed.
Also, in Table 1, Nos. 2, 3, 4 and 5 show the results when the annealing treatment conditions were respectively set to the conditions in the table.
It can be seen that unlike the case of No. 1 above, the Josephson junction is formed by performing the annealing treatment after the film formation. Further, here, it is understood that when the carbon dioxide partial pressure is increased or the cooling rate is decreased, the bonding type is changed from the microbridge type to the tunnel type.

[0016]

[Table 1]

FIG. 3 shows a graph of current-voltage characteristics at 77K of the superconducting junction device obtained under the conditions of No. 2 in Table 1. From this result, it is understood that a good microbridge junction type Josephson device was obtained by the present invention. In addition, also in the device of No. 3 in Table 1, almost the same result as the case of No. 2 was obtained. FIG. 4 shows a graph of current-voltage characteristics at 4.2K of the device obtained in No. 4 of Table 1. From this result, it can be seen that a good tunnel junction type Josephson device was obtained by the present invention. Incidentally, the device of No. 5 in Table 1 obtained almost the same result as that of No. 4.

The composition of the junction of each of the devices No. 2 to No. 5 was analyzed by EPMA and TEM.
Carbonic acid groups are contained in excess, and MCO ₃ (M = Ca, S
r, Ba) were also detected. From the above results, it is possible to obtain a good Josephson junction by the combination of the materials forming the superconducting portion and the junction constituting the superconducting junction device of the present invention, and the annealing condition for the junction thereafter. I know that

Example 2 First, a complex oxide superconductor having a composition shown in Table 2 below and containing a carbonate group was formed into MgO by magnetron sputtering.
A film having a thickness of 400 nm was formed on the substrate under the same conditions as in Example 1. Then, in the same manner as in Example 1, a width of 10 is formed on the superconducting film by photolithography after film formation.
A bridge having a size of 10 μm and a length of 10 μm was prepared. Thereafter, annealing temperature = 800 ° C., oxygen partial pressure = 1 atm, carbon dioxide partial pressure = 0.01 to 0.1 atm, cooling rate = −1 to −10.
° C / min. After performing the annealing treatment under the conditions described above, electrodes were attached and a superconducting junction device having a cross section as shown in FIG. 1 was produced. In order to evaluate the element characteristics of the junction device obtained as described above, a gold wire is attached to the electrode 14 as shown in FIG.
The current-voltage characteristic in the temperature range of 4.2-80K was measured.

Next, as shown in Table 2, various superconducting material compositions were changed to produce superconducting junction devices, and the element characteristics of the superconducting junction devices obtained by the above method were evaluated.
The evaluation results are shown in Table 2, but No. 1 is for comparison.
The result when using the material of Bi-2212 composition which does not contain a carbonate group is shown. As shown in Table 2, the junction in this case was merely ohmic, and was not a Josephson junction. Further, when the superconducting crystal grains were analyzed by EPMA, no portion containing a carbonate group was observed.

In Table 2, No. 2 is an example of using a so-called Bi-CO ₃ type superconducting material, and No. 3 is Tl-.
This is an example of using a CO ₃ -based superconducting material, No. 4
No. 5 is an example of using a so-called 0211-based superconducting material, and No. 5 is a result of an example of using a 1212-based superconducting material. From these results, it can be seen that the Josephson junction is formed by combining the composition and the process of the present invention. At this time, 2
A tunnel type Josephson junction was not obtained in the case of using the Bi—CO ₃ system material and the case of using the Tl—CO ₃ system material, which are considered to have high dimensional properties.
Moreover, when the composition of the junction of the superconducting junction devices obtained in Nos. 2 to 5 was analyzed by EPMA and TEM,
SrBaCuO ₅ C containing a large amount of carbonic acid groups and more carbonic acid groups than the superconducting layer at the junction of the No. 4 device.
However, at the joint of No. 5 device, MCO ₃ (M = Ca,
Sr, Ba) was detected. From the above results, it can be seen that a good Josephson junction can be obtained with the combination of the materials of the present invention.

[0022]

[Table 2]

[0023]

As described above, according to the present invention, (1) a superconducting junction device having good characteristics can be obtained by combining a superconducting material containing a carbonate group and a joining material. (2) By making the content of carbonic acid groups in the junction greater than that of the superconducting material, a superconducting junction device with good characteristics can be obtained simply by changing the annealing conditions for the junction after film formation. In addition, the characteristics can be controlled. (3) A superconducting junction device using high-temperature oxide superconductivity that can be used even with inexpensive liquid nitrogen or a simple cooler can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting junction device of the present invention.

FIG. 2 is an enlarged view of the bridge of the first embodiment.

FIG. 3 is a graph showing the current-voltage characteristics of the device No. 2 in Table 1.

FIG. 4 is a graph showing the current-voltage characteristics of the device No. 4 in Table 1.

[Explanation of symbols]

 11; Superconducting thin film 12; Bridge 13; MgO substrate 14; Electrode 15; Current monitor 16; Driving power supply 21; Superconducting crystal grain 22; Junction 23; MgO substrate

Claims (3)

[Claims] 1. A superconducting joint device comprising a superconducting portion and a joint portion, wherein the superconducting portion is made of a copper oxide superconducting material containing a carbonate group, and the joint portion constitutes the superconducting portion. A superconducting junction device having a part of the composition of an oxide superconducting material, and comprising a non-superconducting material in which a carbonate group is contained in a larger amount than the superconducting material. 2. A copper oxide superconducting material constituting a superconducting part is represented by the following general formula: Ln _a Ca _b Sr _c Bad _d Cu _{2 + e} O _{6 + f} C _g (wherein a + b + c + d = 3, and 0.2 ≦ a ≦ 0.
8 and 0.2 ≦ b ≦ 1.0 and 0.5 ≦ c ≦ 2.
2, 0 ≦ d ≦ 1.6, 0 ≦ e ≦ 0.8, and 0
<F <2, and 0.2 ≦ g ≦ 1), and the non-superconducting material forming the joint is represented by the general formula MCO ₃ (where M is Ca,
The superconducting junction device according to claim 1, which is represented by one or more kinds of elements or atomic groups selected from the group consisting of Sr and Ba. 3. The method for manufacturing a superconducting junction device according to claim 1, further comprising the step of heat-treating the joint portion in an atmosphere in which carbon dioxide and oxygen are mixed. Device manufacturing method.